1. Field of the Invention
The present invention relates to a process of preparing a lamination film having two or more layers of a fixed cholesteric liquid-crystal phase, and a lamination film useful as a light-reflecting film or the like, and a heat shield using the film.
2. Background Art
With the recent increase in interest in environment and energy-related issues, the needs for energy-saving industrial products are increasing; and as one of them, glass and film are desired that are effective for heat shield for windowpanes for houses, automobiles, etc., or that is, effective for reducing heat load due to sunlight. For reducing heat load due to sunlight, it is necessary to prevent transmission of sunlight rays falling within any of the visible range or the infrared range of the sunlight spectrum. In particular, windowpanes for automobiles are required to have high transmittance of visible light from the safety viewpoint, and are additionally required to have a high level of heat shieldability. In some countries, there is a move to control the solar reflectance.
Laminated glass coated with a special metallic film capable of blocking out thermal radiations, which is referred to as Low-E pair glass, is often used as eco-glass having high heat-insulating/heat-shielding capability. The special metallic film may be formed by lamination of plural layers, for example, according to a vacuum-deposition method. The special metallic film formed through vacuum deposition is extremely excellent in reflectivity, but the vacuum process is nonproductive and its production cost is high. In addition, when the metallic film is used, it also blocks electromagnetic waves; and therefore in use in mobile telephones and the like, the metallic film may causes radio disturbance; or when used in automobiles, there may occur a problem in that ETC (electronic toll collection) could not be used. Not only for evading the problem of radio disturbance but also from the safety viewpoint, windowpanes for automobiles are required to have high transmittance of visible light.
There has been provided a method utilizing a cholesteric liquid crystal phase. For example, as disclosed in Japanese Patent No. 4109914, it is possible to reflect the light of from 700 to 1200 nm effectively and selectively by a lamination having a λ/2 plate and, on both of the surfaces of the plate, a cholesteric liquid crystal layer capable of reflecting one circular light.
And, JP-T 2009-514022 discloses an IR-reflective article having a cholesteric liquid-crystal layer. Many trials of using a laminate of plural cholesteric layers in a liquid-crystal display device have been made, and concretely, there are known many trials of efficiently reflecting a light falling within a visible light range. For example, Japanese Patent 3500127 discloses examples of a lamination of a lot of cholesteric layers.
In laminating plural cholesteric layers, there is employed a method of superposing wet coating films of a cholesteric liquid-crystal material one after another through drying, thermal alignment and UV curing thereof. For curing the cholesteric liquid-crystal layer, for example, as exemplified in Japanese patent No. 4008358, there may be generally employed a method of irradiating a polymerizing liquid crystal with UV rays for curing thereof, and for example, there is disclosed a method of forming a wide-area cholesteric liquid-crystal film by controlling the radiation intensity within a predetermined range. Japanese Patent 3745221 discloses a method of forming a continuous wavelength-range polarizing element by laminating plural layers of liquid-crystal molecules to give a multilayer film with so controlling the molecules in each layer as to have the same rotation direction. Japanese Patent 3745221 discloses also an optical element extracting circularly polarized light comprising two cholesteric liquid crystal layers, having different helical pitches and same helical axes, and a transition liquid crystal layer disposed between them. JP-A-2005-115359 discloses a lamination method, and in the method, the fluoroaliphatic-containing copolymer in the first layer may be eluted into the coating composition for forming the second functional layer.